If you don't want to use JB Weld or similar solution to close the hammer slot, then work on the edges of the slot to make it less likely to grab a cap off the nipple. De-burr it, round the edges a bit, and kinda countersink it a bit so it will tend to leave the cap on the nipple. Sometimes this helps. Sometimes. Got to be careful not to remove too much metal; it still has to give the cap a good smack.
Good luck with the Slix-Shot nipples. I did not have good luck with them on my 1851s and 1860s, no experience with the 62s. Went to Tresos and factory hammer springs.
One other trick that appears promising, but not completely confirmed with scientific experimentation, is to get the ball seated as close to the chamber mouth as possible regardless of the size of the powder charge. If using a small powder charge, take up some space with cornmeal or cream of wheat filler, or lube wads, or both. The hypothesis is (and I stress it is only a hypothesis but given to me by some experienced cap and ballers) if the ball is seated deeply in the chamber, then the ball spends more time getting to the barrel, allowing pressure to build up higher. So a deeply seated ball may increase blowback, even though the powder charge is small.
Something to play with.